The present invention relates to a waveguide to transmission line transition for coupling signals between transmission lines and waveguides. Such transitions are commonly used for transmission of microwave and millimeter wave energy. Microwave and millimeter wave energy can be transmitted through a number of different transmission media, including waveguides, microstrip and coplanar transmission lines and coaxial cables. Often times, it is necessary to interface one type of transmission medium with another. For instance, coplanar transmission lines are well suited for the transmission of energy on the surface of a semiconductor integrated circuit, while waveguides are suitable for transmission of energy over larger distances. Thus, a need for a transition between the two media arises.
Conventional transitions and adaptors can be configured in the form of fins, ridges and steps disposed in a waveguide. The ridges, fins, and steps are physically designed to transform the impedance of the waveguide to match that of the transmission line. The structures guide microwaves or millimeter waves from a waveguide into an interface, such as a microstrip transmission line. The performance of transitions with these elements depends critically on the dimensions of the elements. Often, fins and ridges are difficult to manufacture.
Conventionally, coplanar waveguide and microstrip transmission lines have been coupled to waveguides by means of intervening transmission lines such as coaxial lines or finlines. The present invention avoids these intermediate transmission lines and has the advantages of lower fabrication cost, lower reflections, and increased reliability due to the elimination of very small and delicate connections in the case of small wavelength devices, e.g., millimeter wavelengths.
Harris, U.S. Pat. No. 4,544,902 shows a semiconductor probe coupling a coaxial cable to a rectangular waveguide. The reference describes a rectangular waveguide, a coaxial cable, a probe and a connector. A semi-conductor probe from the coaxial connector protrudes through a waveguide wall and is connected to the opposite wall of the waveguide.
Igarashi, U.S. Pat. No. 4,725,793 describes a waveguide to microstrip converter in which a probe is formed, surrounded by a dielectric to keep it structurally stable, in a short circuit waveguide. A microstrip transmission line is formed on a substrate. An end of the probe, which is not on the same substrate as the microstrip transmission line, is connected by soldering to the microstrip line.
Fache et al, U.S. Pat. No. 3,924,204 describes a waveguide to microstrip converter in which a microstrip transmission line penetrates into a waveguide through a slot. The transmission line includes a substrate with a conductor strip disposed thereon. The substrate enters the waveguide approximately one-quarter wave from the short circuit plane of the waveguide. In one embodiment, the substrate apparently extends through the waveguide. The substrate of the probe is positioned in the waveguide so that the plane of the substrate is parallel to the length of the waveguide.
Kostriza et al, U.S. Pat. No. 2,829,348 describes a coupling between a transmission line and a rectangular waveguide. The transmission line could be of a type that comprises a ground planar conductor, a layer of dielectric material, and a line conductor. The transmission line is coupled by extending the line conductor through a slot into the rectangular waveguide. The conductor and dielectric can extend partially or entirely across the waveguide. The probe and transmission line are disposed on the same substrate.
Ponchak and Simons, NASA TM-102477, January 1990 describe a rectangular waveguide to coplanar waveguide transition. A sloping tapered ridge in a top broad wall of the rectangular waveguide protrudes and extends down to contact a groove-like slot which gradually tapers in the bottom wall of the rectangular waveguide. The bottom wall can be formed by a printed circuit board.
Dalman, U.S. Pat. No. 5,017,892 & Cornell University Electronics Letters 21 June 1990, show a microwave waveguide to coplanar transmission line transition made of metal. The top wall of the waveguide is an integral part of the output coplanar waveguide, or coplanar transmission line. A signal entering the waveguide encounters a centrally located tapered fin which is shaped to gradually guide the wave to a slot formed in the top of the waveguide. The fin slopes in such a manner as to become the center conductor of the coplanar transmission line. The sidewalls of the slot provide separate ground planes.
Bellantoni, IEEE 1989 Cornell University, shows a transition from waveguide to coplanar transmission line comprising a test fixture employing a sloping finline.
Prior art devices that use sloping fins are difficult to manufacture to the precise tolerances required for optimum performance and are difficult to position within a waveguide. Microwave transitions are complicated by intervening transmission and adaptor structures imposed between the waveguide and transmission line which can create unwanted reflections.